This invention relates to an internal combustion engine cylinder head structure for engines having variable valve timing and more particularly to an improved control valve and mounting arrangement for such cylinder head.
In order to improve the performance of internal combustion engines over widely varying speed and load ranges, it has been proposed to employ a variable valve timing (VVT) mechanism. With these mechanisms, the phase angle between the crankshaft and the camshaft can be changed so as to adjust the valve timing events. In this way, it is possible to obtain optimum valve timing for a wider range of engine running characteristics and conditions than when fixed valve timing is employed. The variable valve timing mechanism may be associated with either a single camshaft that operates all of the valves, or with either or both of an intake and exhaust camshaft.
The most popular form of VVT mechanism employs a hydraulic actuator that is effective to change the phase angle between the crankshaft and the camshaft. These variable valve timing mechanisms are normally provided at one end of the camshaft with which they are associated. This tends to increase the overall length of the engine.
In addition, it is necessary to provide a valve mechanism for selectively pressurizing or depressurizing various portions of the VVT mechanism in order to obtain the phase angle shift. This requires additional machining, not only for the elements of the valve, but also the passages that interconnect the valve to the variable valve timing mechanism.
If the valve body and passages are formed primarily in the cylinder head, this means that machining operations must be performed in the cylinder head, which is a somewhat awkward procedure.
It has, therefore, been proposed to employ a separate body which forms a dual function of journaling the camshaft and also providing the valve body and flow passages. However, the use of such a separate body tends to itself elongate the engine, particularly if the separate body is fixed to the cylinder head in a manner other than via the cylinder head to cylinder block fasteners. If the same fasteners are employed for fixing this extra valve body to the cylinder head as fix the cylinder head to the cylinder block, then the torque stresses of the hold down bolts may be high enough to deform the fluid passages and valve bores.
It has, therefore, been proposed to employ a separate arrangement wherein the valve body and bearing member is affixed to the cylinder head independently of the bolts or fasteners that fix the cylinder head to the cylinder block. Such an arrangement is disclosed in the co-pending application of Masahiro Uchida, entitled: "Variable Valve Timing Mechanism for Engine", Ser. No. 09/195,356 filed Nov. 19, 1998 and assigned to the assignee hereof.
In addition to providing not only the valve body in which the flow control valve is positioned, it is also necessary to mount an actuator for operating the valve element. That application shows an arrangement wherein the valve elements reciprocate about axes that extend generally parallel to the cylinder bores and hence, permits the mounting of the valve actuating elements in a like direction where they can extend through the cam cover of the engine. However, this gives rise to a number of results which may not be desirable under some circumstances.
First, the valve actuator passes through an element that is not rigidly located relative to the cylinder head, in most instances, and hence, misalignment and binding may occur. Furthermore, there is the problem of sealing.
Even though it is desirable to mount the actuator for the valve in such a position that it can be accessible, the upward projection of the valve actuator does not afford adequate protection, even though it makes the component more accessible.
It is, therefore, a principle object of this invention to provide an improved mounting arrangement for the camshaft of a variable valve timing mechanism in an engine, and wherein the valve element and its actuator are constructed in such a way as to permit a compact engine construction, ease of accessibility for the valve actuator, and protection of the valve actuator from elements and misalignment that could interfere with its operation.